Study describes spread of drug-resistant bug that infects cystic fibrosis patients

Researchers in England say a multidrug-resistant bug that can cause chronic and severe lung infections in patients with cystic fibrosis is spreading globally and becoming increasingly virulent.

The bug, Mycobacterium abscessus (a species of nontuberculosis mycobacteria), is commonly found in soil, water, and dust and was previously thought to be independently acquired by individuals through contact with the environment. But now, the researchers report in Science, investigations indicate that the majority of M. abscessus infections are spreading from patient to patient in clinical settings.

Cystic fibrosis is an inherited condition in a which a defective gene causes the excess secretion of mucus that clogs up the lungs, making breathing difficult and eventually leading to respiratory failure. According to the Cystic Fibrosis Foundation, an estimated 30,000 children and adults in the United States have the life-shortening disease. While cystic fibrosis used to be fatal for young children, many patients now can live into their 20s, 30s, and 40s.

In patients with cystic fibrosis, who are more prone to serious infections because of the mucus clogging their lungs, the M abscessus infection can accelerate decline in lung function and be a roadblock for lung transplants. Because the bacteria are resistant to most antibiotics, infections can be difficult to treat. Between 5% and 10% of cystic fibrosis patients get the infection, but that number has been growing.

Infections spreading between patients

With the incidence of M. abscessus infections on the rise, a research team led by scientists from the University of Cambridge and the Wellcome Trust Sanger Institute decided to explore whether cross infection, rather than independent environmental acquisition, was the culprit. To do so, they generated and compared whole-genome sequences for 1,080 clinical isolates taken from 517 cystic fibrosis patients in the US, UK, Ireland, Australia, Denmark, the Netherlands, and Sweden.

Their analysis showed that while some of the infections were independently acquired, many appear to be genetically linked, with a majority of the patients in all countries infected with clustered isolates. This finding, the authors write, suggests "frequent and widespread infection of patients with closely related isolates."

Further genetic analysis indicated that the infections are spreading from person to person, with infected patients possibly contaminating surfaces in a hospital room or spreading the bacteria to other patients through the air.

In addition, the researchers found that the clustered isolates produced higher rates of chronic infections than the unclustered isolates, are associated with worse clinical outcomes in mice, and appear to be more virulent.

"This mycobacterium can cause very serious infections that are extremely challenging to treat, requiring combination treatment with multiple antibiotics for 18 months or longer," lead author Andres Floto, MD, PhD, from the University of Cambridge department of medicine, said in a university news release. "The bug initially seems to have entered the patient population from the environment, but we think it has recently evolved to become capable of jumping from patient to patient, getting more virulent as it does so."

What Floto and his colleagues don't know, however, is how M. abscessus is spreading around the globe. They say they have seen no evidence of cystic fibrosis patients, or equipment, moving between clinics in different countries. That means healthy individuals could potentially be carrying the bacteria around. Zoonotic or environmental vectors of transmission are also a possibility.

See also:

Nov 11 Science study

Nov 10 Cambridge University press release

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